Indeno-fused ring pyran compounds, such as indeno-fused naphthopyrans are useful as photochromic compounds. Photochromic compounds and materials, such as indeno-fused naphthopyrans, in response to certain wavelengths of electromagnetic radiation (or “actinic radiation”), typically undergo a transformation from one form or state to another form, with each form having a characteristic or distinguishable absorption spectrum associated therewith. Typically, upon exposure to actinic radiation, many photochromic materials are transformed from a closed-form, which corresponds to an unactivated (or bleached, or substantially colorless) state of the photochromic material, to an open-form, which corresponds to an activated (or colored) state of the photochromic material. In the absence of exposure to actinic radiation, such photochromic materials are reversibly transformed from the activated (or colored) state, back to the unactivated (or bleached) state. Compositions and articles, such as eyewear lenses, that contain photochromic materials or have photochromic materials applied thereto (such as in form of a photochromic coating composition) typically display colorless (or clear) and colored states that correspond to the colorless and colored states of the photochromic materials contained therein and/or applied thereto.
The properties, such as photochromic properties, of indeno-fused ring pyran compounds, such as indeno-fused naphthopyrans, can be modified by covalently bonding various groups, such as electron withdrawing and electron donating groups, at one or more ring positions on the fused-ring structure. Examples of properties of photochromic indeno-fused ring pyran compounds that can be modified by various groups being covalently bonded to one or more ring positions thereof include, but are not limited to, fade rate, change in optical density, and dichroic properties. With present indeno-fused ring pyran compounds, such as indeno-fused naphthopyrans, there are a limited number of ring positions to which various property-modifying groups can be covalently bonded.
It would be desirable to develop new photochromic indeno-fused ring pyran compounds that have additional and/or new ring-positions to which various property-modifying groups can be covalently bonded. It would be further desirable that such newly developed photochromic indeno-fused ring pyran compounds have photochromic properties that are at least the same as those of presently available photochromic indeno-fused ring pyran compounds.